To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
In a downlink/uplink of a communication system supporting an orthogonal frequency division multiple access (OFDMA) scheme, inter-cell interference (ICI) may significantly degrade performance of a signal receiving apparatus. Particularly, if a reference signal, e.g., a pilot signal, which is used for the signal receiving apparatus to estimate a channel or to measure a channel is distorted due to influence of the ICI, the performance of the signal receiving apparatus may be significantly degraded.
So, most communication standards supporting an OFDMA scheme, e.g., an LTE use various schemes, e.g., a scheme of differently setting location of a reference signal used in each of cells, a scheme of power boosting a reference signal compared to a data signal, e.g., a data symbol and transmitting the power boosted reference signal, and/or the like.
For example, a downlink of an LTE mobile communication system defines that neighbor base stations shift cell-specific reference signals (CRSs) from a specific CRC on a frequency axis based on different offsets and transmit the shifted CRSs, and each base station may power boost a corresponding CRS using a transmission power greater than transmission power applied to a data signal to transmit the power boosted CRS.
The schemes as described above may decrease a degree of distortion of a reference signal due to ICI thereby preventing relatively large degradation of channel estimation performance and channel measurement performance of a signal receiving apparatus.
However, the power boosted reference signal as described above becomes ICI for a data signal included in a target signal, so a non-Gaussian characteristic of an interference signal occurs due to this. This will be described with reference to FIGS. 1 and 2.
Firstly, relation among an interference signal, a target signal, and a received signal in a general LTE mobile communication system will be described with reference to FIG. 1.
FIG. 1 schematically illustrates relation among an interference signal, a target signal, and a received signal in a general LTE mobile communication system.
Referring to FIG. 1, it will be noted that an interference signal, a target signal, and a received signal in FIG. 1 are shown on a resource block (RB) unit basis. Here, an RB includes at least one resource element (RE).
An interference signal 111 denotes a signal transmitted from a neighbor cell, and the interference signal 111 includes, for example, a physical downlink control channel (PDCCH) signal and a CRS transmitted from the neighbor cell.
Further, a target signal 113 denotes a signal transmitted from a corresponding cell, and the target signal 113 includes, for example, a PDCCH signal and a CRS transmitted from the corresponding cell.
Meanwhile, a received signal 115 denotes a signal which a corresponding signal receiving apparatus, e.g., a user equipment (UE) receives, and the received signal 115 includes the PDCCH signal and CRS included in the target signal 113 and the PDCCH signal and CRS included in the reference signal 111.
In the LTE mobile communication system, location of CRSs is differently set among neighbor cells, so specific REs among REs included in an RB through which the target signal 113 is transmitted may be affected by the CRS included in the interference signal 111, and may be further affected by a PDSCH included in the interference signal 111 according to a situation.
Relation among an interference signal, a target signal, and a received signal in a general LTE mobile communication system has been described with reference to FIG. 1, and ICI distribution for an RE group affected by an interference CRS in a general LTE mobile communication system will be described with reference to FIG. 2.
FIG. 2 schematically illustrates ICI distribution for an RE group affected by an interference CRS in a general LTE mobile communication system.
Referring to FIG. 2, an ICI distribution graph as shown in FIG. 2 indicates an ICI distribution graph for an RE group in a case that a signal receiving apparatus, e.g., a UE uses one antenna port, and the number of neighbor cells is 1. In the ICI distribution graph as shown in FIG. 2, a vertical axis indicates a histogram of ICI, and a horizontal axis indicates a real part of the ICI.
Generally, a CRS is boosted with power which is greater than power applied to a data signal by a preset value, e.g., 12 [dB]. So, a CRS transmitted from a neighbor cell may act as ICI for specific REs among REs included in an RB, i.e., target RB, through a target signal of a corresponding cell is transmitted, so a non-Gaussian of an interference signal occurs due to this.
As illustrated in FIG. 2, it will be understood that ICI 213 for a data region shows a Gaussian characteristic, and ICI 211 for a CRS region shows a non-Gaussian characteristic. In FIG. 2, a reference number 215 indicates a Gaussian probability density function (PDF).
ICI distribution for an RE group affected by an interference CRS in a general LTE mobile communication system has been described with reference to FIG. 2, and a process of performing a channel decoding operation in a signal receiving apparatus in an interference environment with a non-Gaussian characteristic in a general LTE mobile communication system will be described with reference to FIG. 3.
FIG. 3 schematically illustrates a process of performing a channel decoding operation in a signal receiving apparatus in an interference environment with a non-Gaussian characteristic in a general LTE mobile communication system.
Referring to FIG. 3, a signal receiving apparatus calculates an LLR for a received signal at operation 311, and this will be described below.
The signal receiving apparatus detects a data signal which is affected by a target reference signal from the received signal at operation 313, and proceeds to operation 315. Here, the target reference signal denotes a reference signal transmitted from a cell to which the signal receiving apparatus belongs, i.e., a serving cell. The signal receiving apparatus cancels a component related to the target reference signal from the data signal which is affected by the target reference signal at operation 315, and proceeds to operation 317.
The signal receiving apparatus estimates variance of noise which is affected by ICI based on the target reference signal at operation 317, and proceeds to operation 311. The signal receiving apparatus applies a Gaussian PDF based on the estimated variance of the noise to calculate a soft decision decoding metric, e.g., a log-likelihood ratio (LLR) for the received signal at operation 311.
The channel decoding operation of the signal receiving apparatus as described in FIG. 3 is a channel decoding operation in a case that the signal receiving apparatus may not receive location information for a reference signal transmitted from a neighbor cell.
As described above, currently in most communication standards supporting an OFDMA scheme, location of reference signals used in neighbor cells is differently set, so influence of a power boosted interference reference signal is not reflected in the received target reference signal.
So, a channel decoding operation using an LLR calculated based on a scheme as described in FIG. 3 may not reflect influence of power boosted interference reference signal, so the channel decoding operation may significantly degrade channel decoding performance of a signal receiving apparatus.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.